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They are among war’s invisible wounds: the emotional and cognitive problems that many troops experience years after combat explosions sent huge shock waves through their brains. Whereas the link between concussions and post-traumatic stress disorder has become clearer in recent years, a specific connection between PTSD and blast waves has remained elusive.

Now, a prominent neuropathologist who researches brain injuries among military personnel says his team has identified evidence of tissue damage caused by blasts alone, not by concussions or other injuries. The team’s study was published on Thursday in The Lancet Neurology.

The discovery could eventually lead to better treatments and to improved head and body protection for troops exposed to high-energy blasts, some experts said. Other researchers advised that these initial findings should be bolstered by more studies before veterans and their families read too much into them.

”We talk about PTSD being a psychiatric problem — how people responded to the horror of warfare,” said Dr. Daniel P. Perl, the neuropathologist who led the study. ”But at least in some cases, no — their brain has been damaged.”

”The real black box is to figure out who has this,” added Dr. Perl, who works at the Uniformed Services University of the Health Sciences in Bethesda, Md., the medical school run by the Department of Defense.

Even the tentative results provided some solace to Jennifer Collins, who was married to one of the five male military veterans whose damaged brains were examined in the study. Her husband, David, served 17 years in the Navy SEALs, enduring countless explosions in Iraq and Afghanistan. He retired in 2012, and steadily developed significant depression, sleeplessness and memory loss. He killed himself in March 2014.

”This is proof that this man died in combat,” Ms. Collins said in a telephone interview, sobbing and struggling to find words. ”It took several years to kill him, but he died in combat. This finding is further validation about what I know about my husband.”

It is unclear how many of the 2.5 million United States service members deployed to Iraq and Afghanistan were exposed to blasts. A 2008 report by the RAND Corporation suggested that the number could be about 500,000. But some estimates suggest the problem could be greater: For example, a 2014 study of 34 living veterans from those conflicts found that a majority had experienced at least five blasts.

Explosions from roadside bombs, grenades and other devices produce a wide spectrum of injuries. Beyond the shrapnel and other objects that impale the head and body, the hurricane-force wind can blow troops off their feet, causing fatal head injuries and concussions on impact.

Less understood is how the blast wave — the pulse of compressed air that shoots in all directions faster than the speed of sound and arrives before the wind — affects brain tissue after crashing through the helmet and skull. Blasts are also believed to compress the sternum and send shock waves through the body’s blood vessels and up into the brain.

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The researchers examined the brains of the five veterans who had been exposed to blasts, and compared samples with those of 16 other veterans and civilians with and without brain injuries from military service or other activities. Scar tissue in specific locations of the cerebral cortex, which regulates emotional and cognitive functioning, was found only in the blast-injury cases.

All five of those men also suffered from the symptoms of PTSD, which, given the location of the scarring, suggests that a physical combat injury could have led to or exacerbated their psychological troubles, Dr. Perl said. Any such connection, now only speculative and needing further research, could lead to a better understanding of a link between combat and PTSD, said Dr. Ibolja Cernak, the chairwoman of military rehabilitation research at the University of Alberta.

Dr. Cernak likened the blast-injury study published in The Lancet Neurology to the first reports of chronic traumatic encephalopathy among professional football players, whose disease was linked to repetitive on-field brain trauma and helped explain some of their cognitive and emotional problems decades later. As with C.T.E., the damage connected to blasts does not appear on any magnetic resonance imaging test or brain scan and can be located only after death.

”This could be for the military population what C.T.E. was for football players — enormous,” Dr. Cernak said of the research.

Beyond treatment options, the findings raise the possibility that better head protection for active soldiers could ameliorate a blast wave’s damage. Dr. Ralph G. DePalma, a special operations officer in the office of research and development at the Department of Veterans Affairs, called that prospect ”probably the most important aspect of this paper.”

”Looking at the mechanism of how the injury occurs and possible interventions immediately, that’s something that the Department of Defense is very interested in,” Dr. DePalma said. ”We know that certain blast exposures, the angles at which the blast encounters the face and helmet matters. So you can look at protection.”

Some experts are concerned that as significant as identifying blast-related damage in the brain can be, linking it to PTSD is premature. For example, Mr. Collins’s brain also showed signs of C.T.E., which has been found in previous autopsies of military veterans and could have contributed to his psychiatric condition. One of the other four subjects in the study had very small signs of C.T.E., but the other three showed none.

”We have to be very certain — it’s about not jumping the gun, not jumping to conclusions about the significance of the changes we find in the brain in terms of a person’s prognosis or their symptoms,” said Dr. Ann McKee, the chief of neuropathology at the V.A. Boston Healthcare System. She and others at Boston University have identified C.T.E. in the brains of about 100 former N.F.L. players and some military veterans.

”Until we really understand how those changes come about and what the changes really mean,” she added, ”we won’t understand the clinical factors that lead to disability from these diseases.”

Dr. DePalma added that even if no treatments could be developed for years, soldiers should not assume that they would emerge from combat with damage from blast waves. Genetics are believed to influence whether a football player will develop C.T.E., so military combat may pose different risks to different people.